1. Field of the Invention
This invention relates generally to surface temperature-measuring thermocouple probes, and more specifically to insulated, thin-foil, precision, touch-type, passive probes of this type which have a fast-response time and are capable of producing a result containing only a small and readily correctable measurement error, and to a method for making such a probe.
2. Description of the Prior Art
When various thermocouple probes are placed in contact with a hotter surface for measuring surface temperature, thermal energy transfers from the surface of the probe, resulting in cooling of the portion of the goods contacted, thus leading to a reading lower than the actual goods temperature. Further, whatever the surface temperature at the point of contact, the sensor reads lower because of the combined effect of thermal resistance between the contacted surface and the sensing element of the probe plus heat loss from the sensing element to the remainder of the probe and its environment. Any massiveness of the sensing element and associated components causes delay in response and can cause additional error.
A particular long-standing problem is encountered in the measurement of the surface temperature of lightweight sheets of low thermal-conductivity material moving at high speeds. This is especially so when such sheets are hot enough to be sticky or even partially softened.
U.S. Pat. No. 3,332,285 relates to a fast precision temperature sensing thermocouple probe which deals with the problem of thermal energy transferred to or from a thermocouple probe. The probe structure may be in the form of a hand-held probe with an attached extended handle. This, however, is an active device using an electronic circuit to supply heat to the heating element attached to the thermocouple to bring the probe to a temperature equal to that of the goods, thus minimizing the thermal energy flow from the substance being checked to the probe and increasing the validity of the temperature readings.
U.S. Pat. No. 3,671,328 relates to a temperature measuring thermocouple device wherein, in the most pertinent embodiment of the invention, two strips of different semi-conductor materials are mounted on a nonelectrically conducting substrate material such as glass or ceramic which are intermediate conductors of heat. Output lead wires of similar material are connected to the strips of semi-conductor material and to a suitable electric meter or other instrument. Two other leads dissimilar from each other are connected together at a neutral location on the substrate so that all the connections are at the same constant temperature during a measurement.
Other thin-foil heat sensing devices may be found in the following U.S. Patents issued to N. E. Hager, Jr.: Nos. 3,045,473-July 24, 1972; 3,427,209-Feb. 11, 1969; 3,529,473-Sept. 22, 1970; 3,354,720-Nov. 28, 1967; and 3,217,537-Nov. 16, 1965.
The disclosures of the prior art, however, do not teach how to construct and operate a simple, non-massive, passive, fast-response, touch-type pyrometer capable of measuring temperatures of fixed or moving surface areas, particularly those of lightweight low-thermal-conductivity materials without modifying their temperatures through contact with the probe.